Plastic energy management beam

ABSTRACT

An energy-absorbing system includes a tube made of a continuous polymeric material. The tube has first and second tube sections connected by an intermediate tube section. By this arrangement, upon the bumper system receiving a longitudinal impact, the first and second tube sections telescopingly collapse with a predictable and consistent rolling collapse.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/607,677 entitled PLASTIC ENERGY MANAGEMENT BEAM, which was filed Sep.7, 2004, the entire contents of which are hereby incorporated herein byreference.

This application is a continuation-in-part of U.S. Pat. No. 7,021,686,entitled TUBULAR ENERGY MANAGEMENT SYSTEM FOR ABSORBING IMPACT ENERGY,which is a continuation of U.S. Pat. No. 6,942,262, filed Aug. 26, 2003,entitled TUBULAR ENERGY MANAGEMENT SYSTEM FOR ABSORBING IMPACT ENERGY,which is a continuation-in-part of U.S. Pat. No. 6,648,384, filed Sep.27, 2001, now U.S. Pat. No. 6,648,384, entitled CRUSH TOWER WITH RINGSOF VARIED STRENGTH, the entire contents of all of which are incorporatedherein by reference. This application is also a continuation-of-part ofU.S. application Ser. No. 10/808,127, entitled ENERGY MANAGEMENT BEAM,which was filed on Aug. 26, 2003, the entire contents of which arehereby incorporated herein by reference. Finally, this application acontinuation-in-part of PCT Application No. PCT/US03/39803 entitledBUMPER SYSTEM INCORPORATING THERMOFORMED ENERGY ABSORBER, which wasfiled on Dec. 15, 2003, and which claimed priority to U.S. ApplicationSer. No. 60/484,712, the entire contents of both of which areincorporated herein by reference.

BACKGROUND

The present invention relates to energy-management systems configured toabsorb significant impact energy in a consistent and predictable mannerduring an impact stroke, including energy absorbers made of polymericmaterials.

The federal government, insurance companies, and agencies, associations,and companies concerned with vehicle safety have establishedstandardized impact tests that vehicle bumper systems must pass. Bumpermounts and crush towers are commonly used to support bumper bars onvehicle frames and often are used to absorb energy during a vehicleimpact. Several characteristics are beneficial for “successful” bumpermounts and crush towers. It is desirable to manufacture bumper mountsand crush towers that provide consistent and predictable impact strengthwithin a known narrow range, so that it is certain that the bumpersystems on individual vehicles will all pass testing. This letsmanufacturers make a safer vehicle and also lets them more preciselyoptimize their bumper systems to reduce excess weight and to utilizelower cost materials. More specifically, it is desirable to manufacturebumper mounts and crush towers that provide a consistentforce-vs-deflection curve, and to provide a consistent energyabsorption-vs-time curve, and to provide a consistent and predictablepattern of collapse. This lets vehicle manufacturers know with certaintyhow much deflection is created with any given impacting force, and howmuch energy is absorbed at any point during an impact or vehiclecollision. In turn, this allows vehicle manufacturers to design enoughroom around the bumper system to permit non-damaging impact withoutwasting space to compensate for product variation and to provide enoughsupport to the bumper system on the vehicle frame. Theforce-versus-deflection curve has several important ranges at which thecrush tower changes from elastic deformation to permanent deformation tototal collapse and bottoming out. It is important that these variouspoints of collapse be predictable to assure that substantial amounts ofenergy are absorbed before and during collapse, and also to assure thatcollapse occurs before excessive loads are transferred through thebumper system into the vehicle and its passengers.

In addition to the above, bumper development programs require long leadtimes, and it is important that any crush tower be flexible, adaptable,and “tunable” so that it can be modified and tuned with predictabilityto optimize it on a given vehicle model late in a bumper developmentprogram. Also, it is desirable to provide a crush tower design that canbe used on different bumper beams and with different bumper systems andvehicle models, despite widely varied vehicle requirements, so that eachnew bumper system, although new, is not a totally untested and “unknown”system.

Some tubular crush towers are known for supporting bumper beams in abumper system. In one type, two stamped half shells are welded together.However, this process generates raw material scrap. Also, the weldingprocess is a secondary operation that adds to manufacturing overheadcosts. Further, the welded crush towers are subject to significantproduct variation and significant variation in product impact strength,force-versus-deflection curves, energy absorption curves, and crushfailure points.

Some crush towers use stronger materials than other crush towers.However, as the strength of a crush tower is increased, there is atendency to transmit higher and higher loads from the bumper beamdirectly into the vehicle frame. This is often not desirable. Instead,it is desirable that the tower itself predictably crush and collapse andabsorb a maximum of energy over a distributed time period. Inparticular, crush towers that are very high in strength will tend totransmit undesirably high load spikes from the bumper beam to thevehicle frame. This is often followed by a catastrophic collapse of thecrush tower where very little energy is absorbed and where the energyabsorption is not consistent or predictable from vehicle to vehicle.Also, it results in premature damage to a vehicle frame. It isparticularly important that a crush tower be designed to flex and bendmaterial continuously and predictably over the entire collapsing strokeseen by the crush tower during a vehicle crash. At the same time, adesign is desired permitting the use of ultra-high-strength materials,such as high-strength low alloy (HSLA) steels or ultra-high-strengthsteels which have a very high strength-to-weight ratio. As personsskilled in the art of bumper manufacturing know, the idea of simplymaking a crush tower out of a stronger material is often a poor idea,and in fact, often it leads to failure of a bumper system due totransmission of high impact loads and load spikes to the vehicle frame,and also to problems associated with insufficient energy absorption.

Vehicle frames, like bumper mounts and crush towers, are preferablydesigned to manage impact energy, both in terms of energy absorption andenergy dissipation. This is necessary to minimize damage to vehiclecomponents, and also is necessary to minimize injury to vehiclepassengers. Like bumper mounts and crush towers, vehicle frames havelong development times, and further, they often require tuning andadjustment late in their development. Vehicle frames (and frame-mountedcomponents) have many of the same concerns as bumper mounts and crushtowers, since it is, of course, the vehicle frame that the mounts andcrush towers (and other vehicle components) are attached to.

More broadly, an energy absorption system is desired that is flexible,and able to be used in a wide variety of circumstances and applications.It is preferable that such an energy absorption system be useful both ina bumper system, and also in vehicle frames (longitudinal and crosscar), and other applications, as well as in non-vehicle applications.Notably, it is important to control energy absorption even in componentsmade of polymeric materials. For example, injection molded andthermoformed energy absorbers are often used in vehicle bumper systems,such as by placing the polymeric energy absorber on a face of a tubularmetal reinforcement beam. It is also important to control initial energyabsorption, especially as bumpers are made to improve pedestrian safetyduring impact by a vehicle.

Accordingly, an energy management system is desired solving theaforementioned problems and having the aforementioned advantages. Inparticular, an energy management system is desired that providesconsistent impact strength, consistent force-vs-deflection curves,consistent energy absorption (for elastic and permanent deformation),and consistent collapse points and patterns, with all of this beingprovided within tight/narrow ranges of product and property variation.Also, a cost-competitive energy management system is desired that can bemade with a reduced need for secondary operations and reduced need formanual labor, yet that is flexible and tunable.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide an energy managementtube adapted to reliably and predictably absorb substantial impactenergy when impacted longitudinally. The tube comprises a polymericfirst tube section, a polymeric second tube section aligned with thefirst tube section, and a polymeric intermediate tube section with firstand second end portions integrally connecting the first and second tubesections, respectively. The first and second tube sections aredimensionally different in size and the intermediate tube section has ashape transitioning from the first tube section to the second tubesection. The first tube section is larger in size than the second tubesection and includes an outer surface defining a tubular boundary. Thefirst end portion includes a continuous band of material which acts tosupport and maintain a columnar strength of the first tube section uponlongitudinal impact, with the second end portion contrastingly beingconfigured to initiate a telescoping rolling of the second tube sectionduring impact as the first tube section maintains its columnar strength.

Another aspect of the present invention is to provide an energymanagement tube adapted to reliably and predictably absorb substantialimpact energy when impacted longitudinally. The tube comprises apolymeric first tube section having a first resistance to deformation, apolymeric second tube section having a second resistance to deformation,with the second resistance to deformation being greater than the firstresistance to deformation, and a polymeric intermediate tube sectionconnecting the first tube section to the second tube section. Uponundergoing a longitudinal impact, the intermediate tube section and thefirst tube section roll predictably and sooner than the second tubesection upon the intermediate tube section receiving forces from thelongitudinal impact.

Yet another aspect of the present invention is to provide a method ofmaking an energy management tube adapted to reliably and predictablyabsorb substantial impact energy when impacted longitudinally. Themethod comprises molding a polymeric first tube section, molding apolymeric second tube section, aligning the second tube section with thefirst tube section, and molding a polymeric intermediate tube sectionwith first and second end portions integrally connecting the first andsecond tube sections, respectively. The first and second tube sectionsare dimensionally different in size and the intermediate tube sectionhaving a shape transitioning from the first tube section to the secondtube section. The first tube section is larger in size than the secondtube section and includes an outer surface defining a tubular boundary.The first end portion includes a continuous band of material which actsto support and maintain a columnar strength of the first tube sectionupon longitudinal impact, with the second end portion contrastinglybeing configured to initiate a telescoping rolling of the second tubesection during impact as the first tube section maintains its columnarstrength.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a horizontal cross-sectional view of a bumper system includinga mounting plate attached to a vehicle frame, a bumper beam, and a crushtower including opposite ends attached to the mounting plate and thebumper beam;

FIG. 2 is a view similar to FIG. 1, but with the crush tower collapsed afirst (relatively short) distance; and

FIG. 3 is a view similar to FIG. 2, but with the crush tower collapsed asecond (longer) distance.

FIG. 4 is a side view of an energy management tube embodying the presentinvention;

FIG. 5 is a perspective view of additional cross-sectional shapes thatthe energy management tube can take on;

FIGS. 6-8 are side views of a tubular blank with a first diameter (FIG.6), the tubular blank being compressed to a reduced diameter at one end(FIG. 7) and then deformed longitudinally at an intermediate tubesection to take on an S-shaped pre-set (FIG. 8), FIG. 8 showing anenergy management tube of the present invention;

FIGS. 9-11 are side, end, and longitudinal cross-sectional views of thetube of FIG. 8, the tube having an outwardly flared end portion of itsintermediate tube section adjacent its large diameter tube section;

FIG. 12 is an enlarged view of the circled area XII in FIG. 10;

FIG. 13 is a perspective view of the tube shown in FIG. 14, the tubebeing partially telescopingly collapsed and including rolled material onthe larger diameter tube section;

FIGS. 14-15 are side and longitudinal cross-sectional views of amodified energy management tube, the tube having an inwardly flared endportion of its intermediate tube section adjacent its small diametertube section;

FIG. 16 is an enlarged view of the circled area XVI in FIG. 15;

FIG. 17 is a graph showing a load-versus-deflection curve for alongitudinal impact of the tube shown in FIG. 10;

FIG. 18 is a chart showing the effect of annealing on hardness andtensile strength versus a distance from a bottom of the tube of FIG. 10with the tube stood on end and with the intermediate section (rangingfrom about 75 mm to about 95 mm) and the second tube section beingannealed;

FIG. 18A is a graph showing the affect of annealing on material used inthe tube of FIG. 18, the sequence of annealing temperature lines A-Jshowing a gradual reduction of yield strength, a reduction in tensilestrength, and an overall increase in strain and formability based onincreasing annealing temperatures;

FIG. 19 is a perspective view of a vehicle frame incorporating thepresent energy management tube of FIG. 10, including enlargement of fourparticular areas where the energy management system of the presentinvention is used;

FIG. 20 is a perspective view of two cross car beams, one being a crosscar beam used in a vehicle frame located under the vehicle's floor-pan,and the other being a cross car beam used above the vehicle's floor panand used to support vehicle seats;

FIG. 21 is a perspective view of a bumper system incorporating a bumperreinforcement beam and a crush tower supporting the bumper beam on avehicle frame;

FIG. 22 is a perspective view of a cross car beam used to support aninstrument panel; and

FIGS. 23-24 are perspective views showing a crushable support memberexploded from an energy management tube in FIG. 23 and positioned withinthe tube in FIG. 24.

FIG. 25A is a front perspective view of a plastic energy management tube(EMT) of the present invention.

FIG. 25B is a cross-sectional view of the plastic EMT of the presentinvention in an initial position.

FIG. 25C is a cross-sectional view of the plastic EMT of the presentinvention after impact.

FIG. 25D is a graph showing a load v. displacement chart for the plasticEMT of the present invention.

FIG. 26A is a cross-sectional view of a second embodiment of the plasticEMT of the present invention.

FIG. 26B is a graph showing a load v. displacement chart for the secondembodiment of the plastic EMT of the present invention.

FIG. 27A is a cross-sectional view of a third embodiment of a plasticEMT of the present invention in an initial position.

FIG. 27B is a cross-sectional view of the third embodiment of a plasticEMT of the present invention in a first crush position.

FIG. 27C is a cross-sectional view of the third embodiment of a plasticEMT of the present invention in second crush position.

FIG. 27D is a graph showing a load v. displacement chart for the thirdembodiment of the plastic EMT of the present invention.

FIG. 27E is a front view of a modification to the plastic EMT of thepresent invention.

FIG. 27F is a graph showing a load v. displacement chard for themodified plastic EMT of the present invention.

FIG. 28A illustrates a first use of the plastic EMT of the presentinvention.

FIG. 28B illustrates a second use of the plastic EMT of the presentinvention.

FIG. 28C illustrates a third use of the plastic EMT of the presentinvention.

FIG. 28D illustrates a fourth use of the plastic EMT of the presentinvention.

FIG. 29 is a perspective view of a first embodiment of a bumper beamemploying the plastic EMT of the present invention.

FIG. 30A is a perspective view of a second embodiment of a bumper beamemploying the plastic EMT of the present invention.

FIG. 30B is a perspective cut-away view of the second embodiment of thebumper beam employing the plastic EMT of the present invention.

FIG. 30C is a cross-sectional view of the second embodiment of thebumper beam employing the plastic EMT of the present invention.

FIG. 31A is a perspective view of a headliner employing the plastic EMTof the present invention.

FIG. 31B is a cross-sectional view of the headliner employing theplastic EMT of the present invention taken along the line A-A of FIG.31A.

FIG. 32 is a representation of an elevator shaft employing the plasticEMT of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof shall relate to the invention as orientated in FIG. 1. However,it is to be understood that the invention may assume various alternativeorientations, except where expressly specified to the contrary. It isalso to be understood that the specific devices and processesillustrated in the attached drawings, and described in the followingspecification are simply exemplary embodiments of the inventive conceptsdefined in the appended claims. Hence, specific dimensions and otherphysical characteristics relating to the embodiments disclosed hereinare not to be considered as limiting, unless the claims expressly stateotherwise.

It is noted that the present invention includes utilizing the energymanagement technology (EMT) in thermoplastic and thermoset polymericmaterials, with and without filler and reinforcement materials such astalc, glass fibers, and the like.

A vehicle bumper system 10 (FIG. 1) includes a vehicle front bumper beam11 with a mounting bracket, a vehicle frame including a rail mountingplate 12, and a crush tower 13 mounted between the bracket and the plate12. The crush tower 13 comprises a tube made of a continuous contiguousmaterial, such as high-strength heat-treatable steel. The tube has firstand second ring sections 14 and 15 connected by an interconnectingsection 16. The interconnecting section 16 has a frustoconically-shapedportion 17 forming a funnel-shaped ramp. In one mode, the first ringsection 14 is heat-treated to a high material strength, such as about140 KSI tensile strength, which is substantially higher than the secondring section 15, which is kept at about 60 KSI tensile strength. It iscontemplated that the tensile strength of the first ring section 14should be above the tensile strength of the second ring section 15 by asignificant amount, such as about 10%, but preferably should be aboutdouble the tensile strength or about 60 KSI above it. This arrangementprovides the stiffness necessary for the ring section 14 to telescopeonto the ring section 15 and to provide bunching at thefrustoconically-shaped portion 17 of the interconnecting section 16.

By this arrangement, upon the bumper system 10 receiving an end impactparallel a length of the crush tower 13, the first and second ringsections 14 and 15 telescopingly collapse into each other with apredictable and consistent multi-phase deformation sequence where athird ring or small radius pinched section 18 (FIG. 2) begins to formand then does form (FIG. 3) between the first and second ring sections14 and 15. Once the third ring 18 is fully formed, as limited by alength of the interconnecting section 16, material begins to buckle andbunch up at location 20 under the “hook” formed by the section 22. It iscontemplated that additional ring sections and interconnecting sectionscould be provided if a vehicle model has enough room, and additionalenergy absorption is desired before final bottoming out of the crushtower.

The illustrated bumper beam 11 is a tubular beam and is known in theart. For example, see Sturrus U.S. Pat. Nos. 5,092,512 and 5,813,594.However, it is contemplated that the beam could be an open non-tubularbeam as well. Also, the bumper beams can be linear or curved. Dependingon their shapes, mounting brackets or plates can be used to provide arelatively flat mounting surface on the bumper adapted for attachment toa crush tower. (See FIG. 14 of U.S. Pat. No. 5,092,512 and FIG. 4 ofU.S. Pat. No. 5,813,594.) Similarly, at the vehicle-connected end of acrush tower, a variety of different means can be used to provide a pointof attachment for securing the crush towers to a vehicle frame.

The present inventive crush tower 13 is made from a single tubularshape. It is contemplated that the tubular shape initially will berollformed and welded into a permanent tube to have a constant andcircular cross section, with uniform walls having a constant thickness.Nonetheless, it is contemplated that non-circular tubes could also beused in the present invention.

After the tube is formed and cut to a desired length, theinterconnecting section 16 is rolled or stamped to form aninwardly-deformed frustoconically-shaped portion 17 (shaped like afunnel) having a low angle to a centerline 21 of the tube, and aninwardly-deformed radiused “quick-out” portion 22 having a greater angleto the centerline 21. The illustrated frustoconically-shaped portion 17has a relatively linear funnel-shaped segment so that it forms a stifframp for guiding the ring section 15 into the ring section 14 duringimpact. Also, the quick-out portion 22 is radiused and angled so that itundergoes a bending force causing it to roll into an inwardly deformedhook shape (see FIG. 2). The inwardly deformed material forms a uniformcolumnar support for the section 15 that maintains a columnar strengthof the tube section 15. This helps the telescoping action of sections 14and 15 during impact, as discussed below.

The internal cavity 25 within the crush tower 13 is open and stays openduring impact. As a result, a component can be positioned within thecavity 25 without adversely affecting a performance of the crush tower13. For example, a tow hook bushing can be located within the cavity 25,if desired.

In operation, the crush towers 13 are manufactured by making a tube,such as by rollforming, then rollforming or deforming into the tube thereduced-diameter interconnecting section and then by heat-treating thering section 14 (and/or sections 15, 17, and 22). A pair of the crushtowers 13 are then assembled into a bumper system 10 by attachment tothe bumper beam 11, with the crush towers 13 being horizontally andlaterally spaced from each other. The bumper system 10 is then attachedto a vehicle frame.

During impact, the interconnecting section 16 begins to buckle due to alinear strength of the ring sections 14 and 15 along their centerline21. In particular, the frustoconically-shaped portion 17 is driven underthe quick-out portion 22 as the quick-out portion 22 doubles back uponitself, forming an inwardly-deformed hook-like ring that grips theportion 17. The radius of portion 22 as compared to the rest of thematerial of portion 17 helps cause this result. This provides a firststage of collapse at a first (lower) level of energy absorption. As thecrush tower 13 undergoes further telescoping during a long stroke from avehicle crash, an end of the interconnecting section 16 is bent over anddrawn under the remaining material of ring section 14. The third ringsection 18 is formed between the ring sections 14 and 15 as the end ofring section 15 bends and rolls onto an outside surface of tube section15. This sequential collapse and deforming of the various sections 14-16and in particular, the rolling of the material of tube section 14absorbs substantial energy in a very predictable manner and within arelatively narrow range of variation.

It is contemplated that the present crush tower can be made on arollforming machine from a roll of high-strength low alloy (HSLA) steel.Further, it is contemplated that the roll of steel can be high-strengthsteel (such as 70 KSI tensile strength), or an ultra-high-strength steel(such as 80 KSI tensile strength or above). If needed, these materialscan be annealed in selected areas to improve their elongation propertiesor to lower their yield strength (such as 60 KSI tensile strength orlower) and/or can be heat-treated in selected areas for increasedstrength. For example, crush towers having an area at one end with a 60KSI tensile strength and an area at an opposite end with a 120 KSIstrength can be made by either method. The intermediate ring section ispreferably about 60 KSI and similar in strength to the lower strengthring section to better assure a good collapse sequence. It is notedthat, in the present disclosure, the term “heat treat” is considered tobe broader than the term “anneal”, and that the term heat treat includesincreasing or decreasing material properties through use of heat andthermal means. It is also contemplated that the heat-treating and/or theannealing can be done in-line with the rollforming apparatus andsimultaneous with the rollforming as a continuous process. When the stepof annealing is done in-line with and simultaneous with the apparatusand rollforming process, it is beneficial to have the rollformed tubularshape be made so that adjacent crush towers face in opposite directions.For example, where the ring 15 (i.e. the end to be attached to thebumper beam) is annealed from a higher strength to a lower strength, itis beneficial to have two ring sections 15 of adjacent crush towers(i.e. before separation into separated tube sections) be next to eachother so that a single annealing heat can be applied over a wider area.This adds efficiency, control, and line speed to the rollforming processand to the annealing process.

Modification

In the following description, similar components, features, and aspectsare identified with the same identification numbers, but with theaddition of a letter “A”, “B”, etc. This is done to reduce redundantdiscussion.

A modified energy management tube 13A (FIG. 4) is provided that isadapted to reliably and predictably absorb substantial impact energywhen impacted longitudinally. The energy management tube 13A includes afirst tube section 14A, a second tube section 15A that is aligned withthe first tube section 14A, and an intermediate tube section 16A withfirst and second end portions 30 and 31, respectively. The end portions30 and 31 integrally connect the first and second tube sections 14A and15A, respectively. The first tube section 14A is dimensionally larger insize than the second tube section 15A, and has a similar cylindricalcross-sectional shape. However, it is noted that the first and secondtube sections 14A and 15A can be different shapes including rectangular,square, oval, round, or other geometric shapes. (See FIG. 5.) Further,it is contemplated that the tube sections 14A and 15A may have differentcross-sectional shapes along their lengths, especially at locationsspaced away from the intermediate tube section 16A where the tubesections 14A and 15A must be adapted to connect to different structures,such as vehicle frame components and the like. (See FIGS. 19-22.) Theintermediate tube section 16A has a shape transitioning from the firsttube section 14A to the second tube section 15A, and further the firstand second end portions 30 and 31 are dissimilar in shape as noted below(FIGS. 9-12).

The present energy management tube 13A (FIG. 4) is disclosed as beingmade from a sheet of annealable steel material with each of the tubesections 14A, 15A, and 16A being integrally formed together as a unit.The wall thickness can be varied as needed to satisfy functional designrequirements. For example, for bumper crush towers and/or vehicleframes, the thickness can be about 1.5 mm to 4 mm, depending on materialstrengths and the specific application requirements of use. It iscontemplated that the sheet will initially be made into a continuouslong tube by a rollforming machine, and thereafter cut into tubularblanks 60 (FIG. 6) of predetermined lengths. Then, the tubular blankswill have the areas of tube sections 15A and 16A annealed, and thenformed to a shape 61 (FIG. 7) where the second tube section 15A iscompressed to a reduced diameter, with the intermediate section 16Atemporarily taking on a temporary frustoconical shape. It has beendetermined that it is beneficial to fixture and longitudinally deformthe energy management tube 13A to a pre-set condition (FIG. 8), so thatthe intermediate section 16A takes on a particular shape that avoidshigh load spikes during initial impact, as noted below. For automotivebumper systems and frame components, it is preferable that the sheet ofmaterial be a good, reliable grade of steel, such as structural steel.Steels having greater than about 35 KSI yield strength work very well.Steels that can be heat-treated or annealed to achieve optimal yield andelongation properties in selected areas are also excellent candidates,such as structural steels, or high-strength low-alloy steel (HSLAS) orultra-high-strength steel (UHSS).

A specific comment about materials is appropriate. As selected materialsget stronger and harder, with higher yield strengths, higher tensilestrengths and lower elongation values, they often become more sensitiveto tight radius and will tend to resist rolling. Instead, they will tendto break, kink, shear, crack, and/or fracture at tight radii. Thisbreaking problem gets worse as the radii approach a thickness dimensionof the material. The present invention utilizes outward and inwardflaring, clearances, and radii specifically chosen to help deal withthis problem. Various grades of steel are known in the art andunderstood by skilled artisans. The reader's attention is directed toASTM A1008/A and A1008M-01a, and also to ASTM A1011A and A1011M-01a forstandardized industry definitions. Structural steels, such as steelshaving about 25 KSI and above, have strength properties where thequality problems noted above begin to occur. Structural steels aretypically a slightly better grade than cold rolled commercial qualitysteel or hot-rolled commercial quality steel. Nonetheless, especially asthey approach 25 to 35 KSI tensile strength, they tend to have problems.It is specifically contemplated that the present invention will workwell using structural steels, such as steels having a tensile strengthof about 25 KSI or greater, in the above-illustrated energy managementtube 13 (and tubes 13A and 13B). The present invention also is welladapted for and works well for stronger materials of 80 KSI and above,and ultra-high-strength steels (UHSS). Where workability and enhancedrolling of material is desired, these steels can be heat treated orannealed to achieve optimal properties at strategic regions along theenergy management tubes.

It is noted that the various steels discussed herein are intended to beand are believed to be well understood by persons skilled in the art ofsteel materials and in the art of rollforming. For the reader's benefit,it is noted that additional information can be obtained from theAmerican Society for Testing and Materials (ASTM). The terms for steelsas used herein are intended to be consistent with ASTM standards anddefinitions. Nonetheless, it is emphasized that the present technologyis very flexible and adaptable to work with a wide variety of materials.Accordingly, the various terms are intended to be broadly construed,though reasonably construed.

The present concepts are believed to be particularly useful for HSLAsteels, and ultra-high-strength steels (UHSS), such as dual phase steel,tri phase (TRIP) steel, or martensitic materials. The present conceptsare also useful for other engineering grade materials, such as aluminumand even softer materials. The present concepts are particularly usefulwhere high strength materials permit weight reduction through reducedwall thicknesses (i.e. gauge reduction). By being heat treatable, thematerial is inherently more workable and flowable, and/or can be mademore workable and flowable in selected areas. For example, this allows apre-set to be formed in the intermediate tube section 16A with smallradii, yet with less risk of developing microcracks and/or macrocracksand/or splitting, less risk of shearing problems and material separationsuch as shelving, and less risk of other quality defects causing reducedmaterial strength in the area of small-radius bends. The property ofbeing annealed also allows the material to roll without shearing,ripping, or tearing, which is important to achieving maximum energyabsorption during impact and longitudinal crush. (See FIG. 13.)

Notably, a performance of the present energy management tube can beadjusted and tuned to meet specific criteria by numerous methods,including by adjustment of the following variables: material thickness,material type, material hardness and yieldability, annealingtemperatures and conditions, tube diameter and shapes, the particularrolling radius design and the degree of pre-set, use of crushableinserts positioned within (or outside) the tube sections, and otherfactors affecting rolling of material, columnar strength, energyabsorption, and distribution of stress during a longitudinal crushingimpact.

As illustrated in FIGS. 9-12, the first tube section 14A is larger insize than the second tube section 15A. The first tube section 14Aincludes an outer surface defining a tubular boundary 32. The tubularboundary 32 matches a cross-sectional shape of the first tube section14A at an area near the first end portion 30. The first end portion 30includes a circumferentially-continuous band of tightly deformedmaterial 34 that is flared outward radially beyond the boundary 32, suchas at a minimum angle of about 25°. This tightly deformed material 34defines a small radius that effectively forms a “pinched” area thatresists rolling of the material. Also, there is some work hardening ofthe material at the small radius. The small radius (on its concavesurface) is preferably not less than about 0.5 times a thickness of thematerial of the first end portion 30. Thus, it adequately resists atendency to shear or crack. The reasons for the deformed material 34resisting rolling are numerous and subtle. It is believed that the tight“small” radius along with the flared shape forms a uniform ringedsupport for the first tube section 14A that acts to support and maintaina columnar strength of the first tube section upon longitudinal impact.When longitudinally stressed, the tightly deformed material 34 resistsrolling of the material of first end portion 30 and of the first tubesection 14A.

Contrastingly, the second end portion 31 (FIG. 12) has a deformedmaterial 35 defining a relatively larger radius (on its concavesurface), such as at least about 1.0 times a thickness of the materialof the second end portion 31. The deformed portion 35 of the second endportion 31, due to its larger radius, is less resistant to rolling ofthe material of the second tube section 15A and is less supportive ofthe columnar strength of the second tube section 15A. In fact, secondend portion 31 is configured to initiate a telescoping rolling of thesecond tube section 15A during impact as the first tube section 14Amaintains its columnar strength. The fact that the tube sections 15A and16A are annealed, and the first tube section 14A is not annealed,further facilitates and causes this result (although annealing is notrequired to have a tendency of a material to roll). Clearances areprovided for the flow of material as necessary as it rolls. Potentially,the tube sections 14A and 15A can be sized to provide support to eachother during the rolling of material during an impact. The pre-setcondition of the intermediate tube section 16A also is important sinceit helps avoid an initial sharp high load peak, such that the loadquickly levels off as it reaches a predetermined initial level, and thenremains at that level during the impact stroke. (See FIG. 17.)

A second energy management tube 13B (FIGS. 14-16) includes a first tubesection 14B, a second tube section 15B, and an intermediate tube section16B interconnecting the tube sections 14B and 15B. However, tube 13Bdiffers from tube 13A. In tube 13B, the end portion 30B of thelarger-diameter first tube section 14B includes deformed material 34Bdefining a larger radius. Further, the deformed material 34B is notflared outwardly, but instead remains generally within a boundarydefined by an outer surface of the first tube section 14B. Concurrently,the end portion 31B of the second tube section 15B includes deformedmaterial 35B defining a smaller radius. The deformed material 35B isflared inwardly inside of a tubular boundary 32B, such as at a minimumangle of about 12°.

FIG. 13 shows a partial stroke impact where a section of material 36from the first tube section 14B of tube 13B has rolled. (In tube 13A,the second smaller tube section 15A is the one that rolls during animpact as it rolls in a similar manner.)

FIG. 17 illustrates a typical load-versus-deflection curve for tubes 13Aand 14A. While there is some variation in loading during the impactstroke, it will be apparent to a person skilled in the art of designingenergy management systems, such as for bumpers and frames, that the loadquickly comes up to a predetermined level, and stays relativelyconsistently at the selected level throughout the impact stroke. Thearea under the load deflection curve represents actual energy absorption(“AEA”) during an impact stroke. A perfect energy absorption (“PEA”)would be calculated by multiplying the maximum load achieved during animpact (D1) times the full impact stroke (D2). The present energymanagement system provides an exceptionally high efficiency rating (i.e.“AEA” divided by “PEA”). Specifically, the present energy managementtube technology ends up with much higher and more consistentenergy-absorption efficiency rating than known bumper crush towers, dueto a relatively fast initial loading, and a relatively well-maintainedand consistent level of loading continued through the entire impactstroke. Specifically, the present inventive concepts provide surprisingand unexpected consistency and reliability of the load-versus-deflectioncurves, and also provide for consistent and reliable energy absorptionand crush strokes.

FIG. 18 is a chart showing a typical annealed tube such as may be usedto get the result of FIG. 17, and FIG. 18A is a graph showing the affectof annealing on material used in the tube of FIG. 18. The sequence ofannealing temperature lines A-J shows a gradual reduction of yieldstrength, a reduction in tensile strength, and an overall increase instrain and formability based on increasing annealing temperatures. Italso shows a general relationship between tensile strength and yieldstrength, as well as a relationship between those properties and strain.

FIG. 19 is a perspective view of a tubular vehicle frame incorporatingconcepts of the present energy management tube of FIGS. 11 and 15 intoits tubular side members. Four particular areas are shown inenlargements next to the four areas, each illustrating a place where theenergy management system technology of the present invention could beused. However, it is noted that the present technology could be used inadditional areas. Further, in a “real” frame, the locations of use wouldmost likely be in more symmetrical locations on the frame.

The illustrated tube 40 (FIG. 19) is located near a front end of thevehicle frame 39, in a longitudinal portion of the front frame sideframe member, just in front of a front cross car beam. The tube 41 isrectangular in cross section, and includes a single intermediate tubesection (16C) (see FIG. 11) configured to initiate rolling material ofone of the tubes (14C or 15C) during telescoping impact. The energymanagement tube 40 is located in a similar forward location on thevehicle frame. Tube 40 is circular in cross section, and includes asingle intermediate tube section (16D) for initiating rolling ofmaterial during telescoping impact. The tube 4l also includes atransition zone 42 on one end where the circular cross sectiontransitions to a square section for engaging a front (or rear) end of avehicle frame member. Tube 41 could be used, for example, to support avehicle bumper.

The two-ended tube 43 is located at a mid-section of a side of theillustrated vehicle frame. The tube 43 is circular in cross section, andincludes two intermediate tube sections 44 and 45 facing in oppositedirections on opposing ends of a smaller diameter centrally located tubesection 46. The tube 43 further includes two larger diameter tubesections 47 and 48 on each outer end of the intermediate tube sections44 and 45. Further, the larger diameter tube sections transition to asquare cross section at their outer ends. Another energy management tube49 is similar to tube 40, and is located at an end of one side member ofthe vehicle frame. However, instead of being in front of the nearestcross beam, the cross beam 50 is attached directly to the largerdiameter tube section of the energy management tube 49, such as bywelding.

FIG. 20 is a perspective view of two cross car beams, one being a crosscar beam 52 used in the same plane as a vehicle frame. The beam orenergy-management tube 52 is similar to two-ended tube 43, discussedabove. It includes a smaller diameter tube section 53 placed in a middleposition, and two larger diameter tube sections 54 and 55 are attachedto the side members of the vehicle frame. Notably, the ends of the tube13A (or 13B) can be annealed to facilitate reforming to better match thegeometry of the frame rails.

The other energy management system of FIG. 20 includes a pair of tubesections 55 placed as cross car beams but used above the vehicle's floorpan or at least positioned at a location relative to the floor pan wherethe seats can be anchored on them. Each tube 55 is similar to tube 52,in that opposing ends of it are anchored to sides of the vehicle. Eachtube 55 includes a smaller middle tube section 56 and two outer largertube sections 57 and 58. The vehicle includes seats 59 and 60′ withfront and rear outer legs 61 attached to the larger tube sections 57 and58, and with front and rear inner legs 62 attached to the smaller tubesection 56.

FIG. 21 is a perspective view of a bumper system incorporating a bumperreinforcement beam 64 and an energy management tube 65 supporting thebumper beam 64 on a vehicle frame. The crush tower 65 is an energymanagement tube similar to the tube 40 and does not need to be discussedin detail.

FIG. 22 is a perspective view of a cross car beam 67 used to support aninstrument panel 68. The beam 67 includes a single long smaller diametertube section 69, and two larger diameter tube sections 70 at each end.The larger diameter tube sections 70 are attached to a vehiclestructure, such as at the vehicle “A” pillars just in front of the frontpassenger doors. Several collars 71 are positioned on the smallerdiameter tube section 69, for supporting brackets 72 and openedattachment flanges 73. Brackets 72 are used to anchor various items,such as the instrument panel 68, and various components and accessoriesin and around the instrument panel 68.

FIG. 23 is a perspective view showing a crushable insert 75 positionedat an outer end of an energy management tube 76, and ready to be axiallyinstalled therein. The tube 76 includes a small diameter tube section77, a large diameter tube section 78, and an intermediate tube section79 interconnecting them and designed to provide a predetermined rollingof material of the small diameter tube section 77 as the small diametertube section 77 moves rollingly into the large diameter tube section 78upon longitudinal impact. The crushable insert 75 includes structuralrings 80 having circumferential strength and that are adapted toradially support the large diameter tube section 78. The structuralrings 80 are interconnected by thin rings 81 that space the structuralrings 80 longitudinally apart. However, the thin rings 81 have apredetermined longitudinal strength, such that they collapse with apredetermined force upon receiving forces in a longitudinal direction.Thus, the crushable insert 75, when positioned within the energymanagement tube 76 (FIG. 24), initially fits snugly into the largediameter tube section 78 in a manner that prevents rattling. However,during longitudinal impact, as the small diameter tube section 77 ismoved into and toward large diameter tube section 78, the material ofthe small diameter tube section 77 begins to roll and move intoengagement with an end of the crushable insert 75. As the small diametertube section 77 rolls, the thin rings 81 of the crushable insert 75collapse, making additional room for more rolled material. The sequencecontinues, until the crushable insert 75 is fully crushed. During theimpact stroke, the crushable insert 75 engages and helps control thematerial that is rolling. For example, in one test, the crushable insert75 increased the longitudinal load by 10,000 pounds force. Also, testinghas potentially shown that the load can be made more consistent, thusincreasing the efficiency rating (i.e. “AGA” divided by “”PEA”, asdescribed above) of the energy management system.

Thus, the crushable inserts provide additional resistance to rolling oftube section 77 and can be used to tune the performance of the energymanagement tube. The illustrated crushable insert 75 in FIGS. 23 and 24is made of an elastomer material that, upon longitudinal loading, willcrush when imparted by the rolling radius of the intermediate tubesection 79. Convex circular rings 81 are positioned between thickerboundary rings 80. When the crushable inserts are loaded, the rings 80transfer load to the convex region which initiate crush on loading.Outward crushing of the convex region 81 is impeded by the inner surfaceof tube section 78. Similar performance can be achieved when tubesection 78 rolls and tube section 77 maintains column strength. Thecrushable inserts can be made from various materials and differentgeometry can be used to tune the performance of the energy managementtube. Crushable inserts can be used to tune the tube performance insteadof increasing tube diameter or material thickness. Some standard ways totune the performance of the tube can be accomplished by increasing thematerial thickness or increasing the tube diameter. The use of crushableinserts provides an alternative way to tune performance without theaddition of significant cost and without the added penalty of weight.

Further Modification

The reference numeral 113 (FIG. 25A) generally designates anotherembodiment of the present invention, having a plastic energy managementtube. The plastic energy management tube 113 is similar to thepreviously described energy management tube 13A. The plastic energymanagement tube 113 includes a first tube section 114, a second tubesection 115 that is aligned with the first tube section 114, and anintermediate tube section 116 connected to the first tube section 114and the second tube section 115. The first tube section 114 isdimensionally larger in size than the second tube section 115, andpreferably has a similar cross-sectional shape. However, it is notedthat the first and second tube sections 114 and 115 can be differentshapes including hexagonal, octagonal, elliptical, race-track shaped,cylindrical, rectangular, square, oval, round, or other geometricshapes. Furthermore, it is contemplated that the tube sections 114 and115 may have different cross-sectional shapes along their lengths,especially at locations spaced away from the intermediate tube section116 where the tube sections 114 and 115 must be adapted to connect todifferent structures, such as vehicle frame components and the like. Theintermediate tube section 116 has a shape transitioning from the firsttube section 114 to the second tube section 115.

The illustrated plastic energy management tube 113 is preferably made ofa thermoplastics often used in parts for absorbing energy such as PC,PBT, PC/PBT, PC/ABS, and other combinations plastic with each of thetube sections 114, 115, and 116 being integrally formed or moldedtogether as a unit. The plastic energy management tube 113 is preferablymade in an injection mold, although it is contemplated that the plasticenergy management tube 113 can be made in other manners. The wallthickness can be varied as needed to satisfy functional designrequirements. The plastic energy management tube 113 can also include ametal parts 199 insert molded therein to build reinforcing strength ofthe plastic energy management tube 113 and/or to assist in assemblingthe plastic energy management tube 113 to other components.

As illustrated in FIGS. 25A-25C, the first tube section 114 is larger insize than the second tube section 115. The intermediate tube section 116includes a first end portion 130 connected to a top of the first tubesection 114 and a second end portion 131 connected to a bottom of thesecond tube section 115. The illustrated first end portion 130 has aninverted “L” shaped section and the second end portion 131 has a “U” or“J” shaped section and is connected to the first end portion 130. Asillustrated in FIGS. 25B and 25C, the first end portion 130 preferablyincludes additional material 133 extending between the two legs of the“L” shaped section. During crushing of the plastic energy managementtube 113, the second tube section 115 begins telescoping rolling at thesecond end portion 131 of the intermediate tube section 116 to crush theplastic energy management tube 113 as illustrated in FIG. 25C. The firsttube section 114 and the first end portion 130 preferably remainstationary during crushing of the second tube section 115. Theadditional material 133 helps to reinforce the first end portion 130.Therefore, the second end portion 131 is configured to initiate atelescoping rolling of the second tube section 115 during impact as thefirst tube section 114 maintains its columnar strength. Clearances areprovided for the flow of material as necessary as it rolls. Potentially,the tube sections 114 and 115 can be sized to provide support to eachother during the rolling of material during an impact. The second endportion 131 (or the pre-set condition of the intermediate tube section116) also is important since it helps avoid an initial sharp high loadpeak, such that the load quickly levels off as it reaches apredetermined initial level, and then remains at that level during theimpact stroke. The plastic energy management tube 113 uses the rollingof material to create a load versus deflection response that is void ofpeaks and valleys but instead can be designed to produce a flat responseas illustrated in FIG. 25D. A square wave response represents the mostefficient absorption of energy. Upon loading, load increases until thecolumn strength of the structure is reached and then rolling willinitiate. Uniform rolling will happen at a level load until all energyis absorbed.

The reference numeral 113 a (FIG. 26A) generally designates anotherembodiment of the present invention, having a second embodiment for theplastic energy management tube. Since plastic energy management tube 113a is similar to the previously described plastic energy management tube113, similar parts appearing in FIGS. 25A-25C and FIG. 26A,respectively, are represented by the same, corresponding referencenumber, except for the suffix “a” in the numerals of the latter. Thesecond embodiment of the plastic energy management tube 113 a includes asecond tube section 115 a having an inner wall 134 tapering from thesecond end portion 131 a of the intermediate tube section 116 a. Thetapering of the inner wall 134 provides a rising load as illustrated inthe load versus deflection graph of FIG. 26B.

The reference numeral 113 b (FIG. 27A-27D) generally designates anotherembodiment of the present invention, having a third embodiment for theplastic energy management tube. Since plastic energy management tube 113b is similar to the previously described plastic energy management tube113, similar parts appearing in FIGS. 25A-25C and FIG. 27A-27D,respectively, are represented by the same, corresponding referencenumber, except for the suffix “b” in the numerals of the latter. Thethird embodiment of the plastic energy management tube 113 b includes aninner energy management tube section 140. The inner energy managementtube 140 is substantially an inverted version of the first embodiment ofthe plastic energy management tube 113, which is connected by a spanningportion 141 to an end of the second tube section 115 b distal the secondend portion 131 b of the intermediate tube section 116 b. Therefore, theinner energy management tube 140 includes a first tube section 114 b′, asecond tube section 115 b′ and an intermediate tube section 116′.

As illustrated in FIG. 27B, the third embodiment of the plastic energymanagement tube 113 b crushes in the same manner as the first embodimentof the plastic energy management tube 113. Therefore, the second tubesection 115 b begins telescoping rolling at the second end portion 131 bof the intermediate tube section 116 b to crush an outer portion of theplastic energy management tube 113 b as illustrated in FIG. 27B. Thefirst tube section 114 b and the first end portion 130 b preferablyremain stationary during crushing of the second tube section 115 b. Theadditional material 133 b once again helps to reinforce the first endportion 130 b. Therefore, the second end portion 131 b is configured toinitiate a telescoping rolling of the second tube section 115 b duringimpact as the first tube section 114 b maintains its columnar strength.Clearances are provided for the flow of material as necessary as itrolls. Potentially, the tube sections 114 b and 115 b can be sized toprovide support to each other during the rolling of material during animpact. The second end portion 131 b (or the pre-set condition of theintermediate tube section 116 b) also is important since it helps avoidan initial sharp high load peak, such that the load quickly levels offas it reaches a predetermined initial level, and then remains at thatlevel during the impact stroke.

After the outer portion of the third embodiment of the plastic energymanagement tube 113 b has been crushed as illustrated in FIG. 27B, theinner energy management tube section 140 will crush along with acontinuation of a crush of the outer portion of the third embodiment ofthe plastic energy management tube 113 b. Therefore, the first tubesection 114 b′ begins telescoping rolling at a first end portion 131 b′of the intermediate tube section 116 b′ to crush the inner energymanagement tube section 140 as illustrated in FIG. 27C. The second tubesection 115 b′ and a second end portion 130 b′ preferably remainstationary during crushing of the second tube section 115 b. Theadditional material 133 b′ once again helps to reinforce the second endportion 130 b′. Therefore, the first end portion 131 b′ is configured toinitiate a telescoping rolling of the first tube section 115 b′ duringimpact as the second tube section 115 b′ maintains its columnarstrength. Clearances are provided for the flow of material as necessaryas it rolls. Potentially, the tube sections 114 b′ and 115 b′ can besized to provide support to each other during the rolling of materialduring an impact. The first end portion 131 b′ (or the pre-set conditionof the intermediate tube section 116 b′) also is important since ithelps avoid an initial sharp high load peak, such that the load quicklylevels off as it reaches a predetermined initial level, and then remainsat that level during the impact stroke.

The plastic energy management tube 113 b uses the rolling of material tocreate a load versus deflection response that is void of peaks andvalleys but instead can be designed to produce a flat response duringthe crush of the outer portion of the third embodiment of the energymanagement tube 113 b as illustrated between points 145 and 150 in FIG.27D and another higher flat response during the crush of both outerportion of the third embodiment of the energy management tube 113 b andthe inner energy management tube section 140 as illustrated betweenpoints 150 and 160 in FIG. 27D.

In the plastic energy management tubes 113, 113 a and 113 b describedabove, either the first tube section 114 or the second tube section 115can be connected to a support structure such that the plastic energymanagement tubes 113, 113 a and 113 b can be reversible. Furthermore,the inner energy management tube section 140 of the third embodiment ofthe plastic energy management tube 113 b can be positioned in a reverseorientation such that the second tube section 115 b′ is connected to thespanning portion 141. Furthermore, the plastic energy management tube113, 113 a or 113 b could comprise several sections that getprogressively smaller (see FIG. 28C). Moreover, any of the tube sectionscan include tapering walls as described above in the second embodimentof the plastic energy management tube 113 a. Furthermore, any of theplastic energy management tubes 113, 113 a and 113 b could include crushinitiating grooves 177 as illustrated in FIG. 27E, which will provide asinus wave energy curve as illustrated in FIG. 27F. Although the grooves177 are shown as being on the second tube section 115, the grooves 177can be on any of the tube sections.

Applications of plastic energy management tubes 113, 113 a and 113 binclude stand alone crushable structures and/or crushable featuresmolded into larger plastic molded parts without the need for toolingaction and moving parts in the tooling for providing uncuts and blindsurfaces in the molded parts. The size of the parts can be molded to anysize desired and the combination of multiple plastic EMTs can be moldedto work in either parallel, series or configured to encompass a largesurface area. A single plastic EMT 113, 113 a or 113 b can be used as aknee bolster 200 in vehicles in front of the driver's knee 202 asillustrated in FIG. 28A, as a crushable member in front of anotherstructure such as a plastic EMT 113, 113 a and 113 b in front of abumper system 210 and behind facia 212 as shown in FIG. 27B, as a bumperbracket between a support frame 220 of a vehicle and facia 222 as shownin FIG. 28C, as an inside component to A and B pillars of a vehicle (notshown), as a highway embankment to protect supports 240 for a bridge 242as shown in FIG. 27D or in other manners. Furthermore, a grouping ofplastic EMTs can be used across a face of a bumper 300 as an energyabsorber as shown in FIG. 29 or within a beam 400 (e.g., the beamdisclosed in U.S. patent application Ser. No. 10/808,127 entitled ENERGYMANAGEMENT BEAM, the entire contents of which are herein incorporatedherein by reference) as shown in FIGS. 30A-30C, or used within aheadliner of a vehicle for head protection as shown in FIGS. 31A and31B. Furthermore, the plastic energy management tube 113, 113 a or 113 bcan be used in a bottom of an elevator shaft 500 to absorb energy of adropping elevator 502 as shown in FIG. 32. Basically, anywhere thatenergy absorption is needed either as a stand alone structure or forlarger areas where an area is required to provide energy absorption, theplastic EMT technology can be used.

The advantages of using plastic to fabricate the part includeflexibility to mold complicated shapes and mold in complex features thatcan be used to tune the performance of the invention. The plastic EMTdoes not need a larger tube having an outwardly flared larger diametersection that promotes telescoping of the smaller diameter section intothe larger diameter section due to the ability to change thickness inthe molding process. The plastic molding process is extremely flexible.Simple single or multiple EMT structure parts are easily molded insimple in/out dies. More complex structures that include internalstiffening ribs and vanes may require a die that incorporates action.The flexibility of molding plastic allows for the specification ofmaterial thickness where it is needed. Changes in thickness can be usedto provide column strength and desired rolling loads. The ability tochange thickness of the plastic and the flexibility provided by themolding process illustrate the advantage associated with the use ofplastic. EMTs can also be molded within and nested within other EMTs tocreate additional load tuning capability (see FIG. 28B).

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

1. An energy management tube adapted to reliably and predictably absorbsubstantial impact energy when impacted longitudinally, comprising: apolymeric first tube section; a polymeric second tube section alignedwith the first tube section; and a polymeric intermediate tube sectionwith first and second end portions integrally connecting the first andsecond tube sections, respectively; the first and second tube sectionsbeing dimensionally different in size and the intermediate tube sectionhaving a shape transitioning from the first tube section to the secondtube section; the first tube section being larger in size than thesecond tube section and including an outer surface defining a tubularboundary, the first end portion including a continuous band of materialwhich acts to support and maintain a columnar strength of the first tubesection upon longitudinal impact, the second end portion contrastinglybeing configured to initiate a telescoping rolling of the second tubesection during impact as the first tube section maintains its columnarstrength.
 2. The energy management tube defined in claim 1, including abumper beam attached to a free end of one of the first and second tubesections.
 3. The energy management tube defined in claim 1, including avehicle frame attached to at least one of the first and second tubesections.
 4. The energy management tube defined in claim 1, including across car frame member attached to at least one of the first and secondtube sections.
 5. The energy management tube defined in claim 1, whereinthe first and second tube sections have similar geometriccross-sectional shapes, but are different cross-sectional sizes.
 6. Theenergy management tube defined in claim 1, wherein at least one of thefirst and second tube sections includes a round cross section.
 7. Theenergy management tube defined in claim 1, wherein at least one of thefirst tube section and the second tube section comprises a wall having avarying thickness.
 8. The energy management tube defined in claim 1,further including at least one metal component molded into at least oneof the tube sections.
 9. The energy management tube defined in claim 1,wherein at least one of the first tube section and the second tubesection includes at least one crush initiating groove.
 10. The energymanagement tube defined in claim 1, wherein the first tube sectionincludes a first end area having a greater thickness than the rest ofthe first tube section, the second tube section and the intermediatetube section.
 11. The energy management tube defined in claim 10,wherein the first end area abuts the intermediate tube section.
 12. Anelevator system comprising an elevator shaft having a bottom and theenergy management tube defined in claim 1 located therein.
 13. A driverprotection system comprising a bridge pillar having the energymanagement tube defined in claim 1 located in front of the bridgepillar.
 14. An energy management mat comprising a plurality of energymanagement tubes defined in claim
 1. 15. An energy management tubeadapted to reliably and predictably absorb substantial impact energywhen impacted longitudinally comprising: a polymeric first tube sectionhaving a first resistance to deformation; a polymeric second tubesection having a second resistance to deformation, the second resistanceto deformation being greater than the first resistance to deformation;and a polymeric intermediate tube section connecting the first tubesection to the second tube section; whereby, upon undergoing alongitudinal impact, the intermediate tube section and the first tubesection roll predictably and sooner than the second tube section uponthe intermediate tube section receiving forces from the longitudinalimpact; and wherein the second tube section is larger in size than thefirst tube section, the intermediate tube section being configured toinitiate a telescoping rolling of the first tube section during impactas the second tube section maintains its columnar strength.
 16. Theenergy management tube defined in claim 15, including a bumper beamattached to a free end of one of the first and second tube sections. 17.The energy management tube defined in claim 15, including a vehicleframe attached to at least one of the first and second tube sections.18. The energy management tube defined in claim 15, including a crosscar frame member attached to at least one of the first and second tubesections.
 19. The energy management tube defined in claim 15, whereinthe first and second tube sections have similar geometriccross-sectional shapes, but are different cross-sectional sizes.
 20. Theenergy management tube defined in claim 15, wherein at least one of thefirst and second tube sections includes a round cross section.
 21. Theenergy management tube defined in claim 15, wherein at least one of thefirst tube section and the second tube section comprises a wall having avarying thickness.
 22. The energy management tube defined in claim 15,further including at least one metal component molded into at least oneof the tube sections.
 23. The energy management tube defined in claim15, wherein at least one of the first tube section and the second tubesection includes at least one crush initiating groove.
 24. The energymanagement tube defined in claim 15, wherein the second tube sectionincludes a first end area having a greater thickness than the rest ofthe second tube section, the first tube section and the intermediatetube section.
 25. The energy management tube defined in claim 24,wherein the first end area abuts the intermediate tube section.
 26. Anelevator system comprising an elevator shaft having a bottom and theenergy management tube defined in claim 15 located therein.
 27. A driverprotection system comprising a bridge pillar having the energymanagement tube defined in claim 15 located in front of the bridgepillar.
 28. An energy management mat comprising a plurality of energymanagement tubes defined in claim
 15. 29. An energy management tubeadapted to reliably and predictably absorb substantial impact energywhen impacted longitudinally comprising: a polymeric first tube sectionhaving a first resistance to deformation; a polymeric second tubesection having a second resistance to deformation, the second resistanceto deformation being greater than the first resistance to deformation;and a polymeric intermediate tube section connecting the first tubesection to the second tube section; whereby, upon undergoing alongitudinal impact, the intermediate tube section and the first tubesection roll predictably and sooner than the second tube section uponthe intermediate tube section receiving forces from the longitudinalimpact; and wherein the second tube section includes a first end areahaving a greater thickness than the rest of the second tube section, thefirst tube section and the intermediate tube section.